Problems managing representative freshwater reserves
David Eccles 23/1/2001
I certainly agree that representative reserves are important to maintain biodiversity. However, I fear that these may not be possible in many freshwater ecosystems. This is because a water body integrates the character of its catchment so that, unless the catchment is itself preserved, it may be impossible to return to a 'normal' ecological situation.
This is not such a problem in terrestrial systems where, as long as the reserve is large enough to be self-sustaining, extraneous influences are less important.
I do not know how this can best be addressed. In the case of habitats within protected areas no further action is necessary, except perhaps to prevent upstream migration of aliens while allowing it for natives. The most important areas for conservation are those parts of systems outside, but immediately downstream from, protected areas. These should be given priority for action as they are likely to be least affected by upstream processes.
These observations are based on my experience of the breeding of migratory freshwater fishes in Africa, many of the populations of which have been destroyed. I believe this has been due to smothering of the eggs, usually laid in flooded grassland or on gravel beds, by sediment from disturbed land.